English proficiency difference among students is a challenging pedagogical issue in EFL classrooms worldwide. Collaborative digital storytelling has been adopted in language learning settings to increase motivation and engagement, especially for young learners. However, it remains unknown whether students of different proficiency levels can equally benefit from this collaborative approach. Thus, this study implemented a 17-month technology-enhanced collaborative storytelling activity and examined young students' pair performance, flow perception, and learning strategies in relation to students' English proficiency level. The students' proficiency level was found to be an influencing factor of their engagement patterns, use of learning strategies, and pair performance. These findings support the low-threshold-high-ceiling principle, suggesting that collaborative activities should ensure students of different proficiency share the same goals, while allowing different types of participation to maximize their engagement. It is hoped that the findings and pedagogical suggestions can address the issue of proficiency differences in EFL classrooms and serve as a reference for future research of EFL collaborative storytelling activities.